Structural Design and Optimization of Asphalt-Overlaid Concrete Slabs under Dynamic Loading

The rehabilitation of damaged concrete pavements often involves asphalt overlays, yet the interaction between damage severity, overlay thickness, and loading conditions remains insufficiently quantified. This study investigates the combined effects of asphalt overlay thickness, concrete damage, and applied load on the structural performance of pavement slabs, providing insights for optimizing overlay design. Twenty-one concrete slabs (120 × 50 × 15 cm; 0.09 m³) were cast with varying cement contents (100–300 kg/m³) to simulate five damage levels (D0%, D20%, D40%, D60% and D80%) and a high-strength control. Within each damage group, specimens were either left uncoated or overlaid with asphalt layers of 4, 6, 8, or 10 cm. Compressive strength testing confirmed the intended gradient, with load capacities ranging from 45 kN (D20%) to 220 kN (D0%). Cyclic loading (450 cycles, 2–0.1 tons) followed by incremental static loading quantified strain and vertical settlement. Increasing asphalt thickness significantly reduced surface strain—from >600 µε for 4 cm overlays to ~150 µε for 10 cm—but increased vertical deformation (from -9 mm to ~-21 mm). Regression modeling (R² = 0.9726 for strain; R² = 0.9997 for deformation) revealed a nonlinear, interaction-driven system where applied load was the dominant factor (+7.17 µε/kN strain; −0.607 mm/kN deformation, p < 0.001), while thickness reduced strain (r = −0.420) but increased compliance (r = −0.683). Among tested configurations, a 6 cm overlay achieved the optimal balance, reducing strain by 70–82% while maintaining controlled deformation and stable cyclic creep.